Session: 12-26-01: Mechanics and Materials of Soft Electronics

Paper Number: 150551

150551 - Highly Stretchable and Customizable Microneedle Electrode Arrays for Intramuscular Electromyography 

Microneedle electrode arrays have been a widely used technological platform for biomedical applications such as electrophysiological sensing and electrical stimulation. They can penetrate surface layers of tissues, thereby allowing probing of physiological signals and electrical stimulation of the deep tissues in a minimally invasive manner. Stretchable microneedle electrode arrays (SMNEAs) are highly desirable as dynamic bioelectrode interfaces to tissues or organs as they can follow tissue deformations, which enhances recording signal quality and reduces tissue damage. However, fabricating custom stretchable 3D microelectrode arrays presents significant material integration and patterning challenges. In this talk, we will present the design, fabrication, and applications of SMNEAs for sensing local intramuscular electromyography signals ex vivo.

We first developed a low-cost and scalable microneedle electrode fabrication process combining laser micromachining, replica molding, microfabrication, and transfer printing, that allows the formation of individually addressable, high-modulus microneedle arrays connected to serpentine-shaped interconnects. Covalent bonding of the microneedles and interconnects to an elastomeric substrate yields high stretchability. Metallization and a gel-based chemical etching technique applied to the microneedles yield microneedle electrode arrays with controllable exposed areas. The fabrication scheme uniquely combines scalability with varying electrode lengths, controlled recording regions and electrode impedance, device stretchability of 60-90%, and relatively large electrode modulus (E =  6.6 GPa).

We then developed a lithography-free fabrication scheme that combines 3D printing, physical vapor deposition, and transfer printing, which enables scalable fabrication of SMNEAs with over 100% stretchability. A vat photopolymerization process creates polymeric microneedle arrays with custom geometries connected by a thin layer of serpentine filaments, followed by transfer printing onto a stretchable elastomer and metallization for electrical connection. This new process further simplifies the fabrication and customization with increased device stretchability.

We demonstrated that these SMNEAs with customized geometries and layouts can penetrate various muscle groups in the buccal mass of Aplysia. Highly localized intramuscular electromyography signals were recorded at the individual muscle level from the SMNEA, which can follow the deformations of the buccal mass. Penetrating microneedle electrodes with different lengths and exposed microscale tips can target the interior of tissues, while the stretchability of the SMNEA device allows stable electrode-tissue interfacing during movements, contributing to a higher signal-to-noise ratio. In contrast, planar microelectrode arrays that are laminated on the surface of the buccal mass show relatively weak and similar EMG signals across all electrodes. This SMNEA platform may find applications in electrophysiological sensing in brain-machine interfaces, electrochemical sensing of skin interstitial fluids, and electrical stimulation of nerves and muscles.

Presenting Author: Hangbo Zhao University of Southern California

Presenting Author Biography: Dr. Hangbo Zhao is an assistant professor in the Department of Aerospace and Mechanical Engineering and the Afred E. Mann Department of Biomedical Engineering at the University of Southern California, working on micro- and nanomanufacturing, and bio-integrated electronics. Prior to joining USC, he was a postdoctoral researcher at Northwestern University. He received his M.S. and Ph.D. degrees in Mechanical Engineering at MIT, and his bachelor’s degree at Tsinghua University in China. Dr. Zhao has received several awards including the ONR Young Investigator Award, SME Outstanding Young Manufacturing Engineer Award, and ASME Haythornthwaite Foundation Young Investigator Award.

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